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Author Topic: Highest power HT?  (Read 18171 times)
LETTERX
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« on: August 31, 2010, 11:03:40 AM »

Was a VHF or UHF HT ever been produced that has an output power of more than about 5 watts?  Is there any reason why a handheld radio couldn't be made with an output of say 25W?  It wouldn't obviously have a shorter battery life, and be a bit larger/heavier, but heat dissipation should be manageable, I think.  Has anyone ever modified an HT to have significantly higher output power?

This is something I've been wondering about.  Seems that handheld VHF/UHF radios of all kinds - ham, business, marine, recreation - they all have a maximum output of around 5 watts, and I'm just wondering if there's a reason why that is.
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KG4RUL
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« Reply #1 on: August 31, 2010, 11:46:32 AM »

Why not 25W?

  • * Weight - Probably 5# or more to have decent battery life
  • * Heat - My Wife's VX-5R gets uncomfortably hot at 5W
  • * Size - Gonna need a big hand or pocket

As far as what IS available, the iCOM IC-V85 at 7W is probably King-of-the-Hill.
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LETTERX
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« Reply #2 on: August 31, 2010, 12:47:29 PM »

Okay, yeah, makes sense.  I was thinking of a high-power mode that could be switched on and used briefly just to get a message heard, so heat and battery life wouldn't really be an issue.  Seems like a handheld like this would be ideal for emergency situations in RF-difficult locations (under a building, in a tunnel, between mountains, etc.).  Perhaps it could be activated by a second, small PTT button on the other side of the radio, so you have squeeze them both for the high-power emergency "punch" mode.

I was thinking another amp stage based on a 25W Mosfet.  Couldn't that be made pretty small, even with a tiny heatsink?  Like I said, sort of a high-power emergency mode.  Maybe limited to a 10-second TX, or something like that.  You obviously wouldn't want to chew the fat on a small 25W handheld without an oven mitt.

Maybe there's no commercial demand for a radio like this, but is it possible?
« Last Edit: August 31, 2010, 01:46:26 PM by David Monroe » Logged
AA4PB
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« Reply #3 on: August 31, 2010, 01:08:35 PM »

The mfgs probably wouldn't like a high power emergency mode because it would have to have a limited duty cycle. People would be cooking them and sending them back expecting warranty repair  Cry

The other option I guess would be an internal temp sensor that would force it to low power until it cooled off  Grin  but then you'd have those who didn't understand why the HT lost contact after 60 seconds   Huh

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Bob  AA4PB
Garrisonville, VA
K5LXP
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« Reply #4 on: August 31, 2010, 02:20:27 PM »

Technically there's no reason you couldn't build one, but at powers above 5 watts there is an RF exposure safety hazard with an antenna that close to ones' body.


Mark K5LXP
Albuquerque, NM

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LETTERX
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« Reply #5 on: August 31, 2010, 05:28:07 PM »

True, but the RF field strength decreases exponentially (proportional to the cube of the distance?).  So, I could be wrong about this, but I have a feeling there's more of a potential health risk from people literally touching cell phone antennas emitting 2 watts @ 850-900 MHz, and/or 1W @ 1800-1900 MHz.
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K5LXP
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« Reply #6 on: August 31, 2010, 07:52:33 PM »

Well, the question was why you don't see >5W handhelds, and the answer is exposure hazard, one, and at 5W you reach a practical limit of size and practicality.  A rough guess is that 25W into a 0dBi antenna puts the safe range at about 3 feet away.  Not to mention the size of the battery you'd need for the ~75W or so power draw on a battery at that output level.  That's an awful heavy box to be holding out at arm's length.

As to the notion of what's "safe" or not is a separate question, but part of the responsibility of a license holder is to do a station audit for RF exposure levels and certify that they're safe.

Wouldn't take a lot to strap a gel cell onto a 25W mobile and carry it around for a while if you'd like to get a feel for how that kind of setup works.  Not sure where you'd put the belt clip though.


Mark K5LXP
Albuquerque, NM
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LETTERX
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« Reply #7 on: August 31, 2010, 08:23:11 PM »

Wouldn't take a lot to strap a gel cell onto a 25W mobile and carry it around for a while if you'd like to get a feel for how that kind of setup works. 

That's interesting, because I was thinking that the amp stage alone of a 25W mobile rig isn't all that big, and could be reduced in size further with different packaging to better fit a handheld chassis.  I see your point about the battery, though.  I guess a battery-powered amp with BNC connectors to fit on top of an HT is out of the question. <grin>
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WB2WIK
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« Reply #8 on: September 01, 2010, 09:24:58 AM »

True, but the RF field strength decreases exponentially (proportional to the cube of the distance?).  So, I could be wrong about this, but I have a feeling there's more of a potential health risk from people literally touching cell phone antennas emitting 2 watts @ 850-900 MHz, and/or 1W @ 1800-1900 MHz.

There's a lot more to it than that.  These phones only use the power required to hold the circuit and although GSM is 2Wpk and CDMA is usually 1Wpk, these are peak, low duty-cycle ratings.  Average powers run in the 30-300mW range, and the antennas are in the -6 to -10 dBi range, further reducing effective radiated power.

VHF/UHF hand helds that hams use are generally analog FM with a 100% duty cycle for transmission, and the antennas are in the -3 dBi range.

The Specific Absorption Rates are based on effective radiated power, frequency, proximity and duty cycle.

Below is a listing of all the people who have become sick due to the use of hand held cellular telephones:




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AA4PB
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« Reply #9 on: September 01, 2010, 10:13:06 AM »

Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:
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Bob  AA4PB
Garrisonville, VA
KG4RUL
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« Reply #10 on: September 01, 2010, 12:06:33 PM »

Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:


Patiently waiting for the other shoe to drop  Roll Eyes
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WB2WIK
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« Reply #11 on: September 01, 2010, 02:08:33 PM »

Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:


They require you to stare at a white space? Cheesy
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AA4PB
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« Reply #12 on: September 01, 2010, 03:37:11 PM »

Given that the HT is less than 50W PEP output and given that it uses push-to-talk, here is what the FCC requires you to do:


Answer: Nothing. Radios under 50W PEP and mobile/portable stations using PTT control are exempted from the RF exposure requirements.
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Bob  AA4PB
Garrisonville, VA
KC8WUC
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« Reply #13 on: September 02, 2010, 04:58:47 AM »

Icom has made and continues to make a 7w VHF HT- the ICV82 and predecessor, the V85.  I've owned the V85  (I forget the exact nomenclature/model),  which put out a considerably strong signal that seemed to reach well beyond what would be expected of a HT (in excess of 50 miles from the third story of my home).  This radio did have a significant downside, the weight of battery and heat generated from operating made talking on this for more than a minute or two less than comfortable.  I imagine that I also received a fair amount of RF radiation as well. 

I've since given up on using HTs and have restricted my operations to remote mounted mobile (marine) and desk top base stations.

73,

Michael  KC8WUC/WDE9344

Toulon, France
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LETTERX
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« Reply #14 on: September 02, 2010, 05:30:02 AM »

I understand Icom makes some 7W HT models, but the effective gain between 5W and 7W is really negligible, and it's why I said "about" 5W in the original post.  I still think a modern 25W Mosfet-based HT is do-able, and could be made about the same size as the average business hand-held of 25 years ago.  You know, those old low-VHF Motorola talkies that police used to have clipped to their belts in the 80's.  When I was a kid, our local police department operated on 39.020 MHz, and their radios were about the size of a small red building brick.  Probably weighed the same, too, with half of that weight being the NiCad pack.
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